A number of medical treatments include the insertion of catheters, implants, or other devices into the patient's blood stream. Such contact with the blood may cause thrombus formation and subsequent embolization. Various therapies may be used to limit these consequences, including the infusion of heparin or other anticoagulants into the bloodstream.
In one example, radiofrequency (RF) ablation can be used to treat various arrhythmias including atrial fibrillation, ventricular tachycardia and supraventricular tachycardia. RF ablation can be performed percutaneously, a procedure in which a catheter is introduced into the patient through an artery or vein and directed to the atrium or ventricle of the heart to perform one or more procedures. In such circumstances, the RF ablation procedure is used to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities or create a conductive tissue block to restore normal heart rhythm. Successful ablation of the conductive tissue at the arrhythmia initiation site may terminate the arrhythmia or reduce the frequency of the arrhythmia to acceptable levels. When multiple applications of energy are required to treat a clinical arrhythmia (e.g., atrial fibrillation or ventricular tachycardia), thrombus formation and subsequent embolization giving rise to stroke or other embolic sequelae become an important limiting factor. In an effort to limit such complications, therapy such as intravenous anticoagulation can be employed (e.g., infusion of heparin or other anticoagulants to the blood).
Although heparinization can reduce the chance of thrombus formation associated with denuded endothelium, stroke and other thromboembolic events may occur despite adequate heparinization. For example, during RF ablation clotted components (e.g., coagulum) of blood may form along the tip portion of the ablation catheter and the ablated tissue, increasing the effective impedance between the ablation catheter and tissue and also increasing the risk of embolization of the coagulum. One reason is that RF ablation is associated with a direct conversion of fibrinogen to fibrin and subsequently to char. This fibrin and char can potentially lead to embolization even in the absence of thrombin. Accordingly, the coagulum can be formed during RF ablation even if heparin is adequately supplied to reduce thrombin in the blood.